1. Field of the Invention
The present invention relates to a sealing structure in an exhaust system of an internal combustion engine, including a gasket which is clamped between a cylinder head and a flange which is fastened to the cylinder head. The gasket has a sealing portion surrounding an exhaust port opening into a side of the cylinder head. An exhaust pipe which is curved, is coupled to the flange and is in communication with the exhaust port.
2. Description of the Prior Art
Sealing structures in exhaust systems are conventionallly known, for example, from Japanese Utility Model Application Laid-Open No. 10249/88. In the known sealing structure, a bead portion is provided as a sealing portion in a gasket clamped between the cylinder head and the flange to surround the exhaust port, wherein the distance between the bead portion and a peripheral edge of the exhaust port is uniform in the circumferential direction.
However, the exhaust pipe is in close proximity to the flange in the area corresponding to the projected position of the exhaust pipe on the flange, and hence, at such location, heat from the exhaust pipe may be transferred to the flange. Moreover, heat may be accumulated in a space between the curved exhaust pipe and the cylinder head or a cylinder block. For this reason, when the gasket having the sealing portion which surrounds the exhaust port with a circumferentially uniform distance between the sealing portion and the peripheral edge of the exhaust port, is used as in the known sealing structure, the temperature of the sealing portion rises to a higher level in the area corresponding to the projected position of the exhaust pipe on the flange and hence, such area of the sealing portion is liable to be deteriorated, as compared with other areas. To prevent the deterioration of the sealing portion, the distance between the sealing portion and the peripheral edge of the exhaust port may be set at a relatively large value. However, if the distance is made large, the size of the gasket itself is increased and there is a need for increasing the size of the flange, and the distance between exhaust ports in the cylinder head. This results in an increased size of the engine body.